Paul Carmody's Instructions for Frequency Response Modeler

[Rand]

Hi,
I am hoping I can get some help with my project. I’m retrofitting some old 2 way JBL boxes with new drivers and I’m at the stage of designing the new crossover. While learning how to use WinPCD and wondering how I’m going to compensate for the enclosure’s effects, I discovered Jeff Bagby’s Frequency Response Modeler Excel sheet. I also found Paul Carmody’s webpage for instructions on tracing graphs to make zma and frd files all the way to using the FRM Excel sheet to do just what I need.

Parts Express provided the zma and frd files for my woofer the Dayton Audio RS225P-8, and the webpage http://www.audiodevelopers.com/Referenc ... r=PE_DK%2F had them for my tweeter the Dayton Audio DC28F-8. I also have DATS V2 and can make my own zma files.

My first question is about Paul Carmody’s Step #5 instructions for creating the woofer’s simulated zma file using the FRM Excel sheet. Am I correct that you do not import and then modify the woofer’s anechoic zma file made by tracing or other means, but rather have the FRM Excel sheet create a completely new one from the data in the Impedance Model section?

My main problem and second question is about Paul’s Step #6. With all of my woofer and enclosure data filled in, all of the graphs look good except the top 2 in the Frequency Response Modeler section which just have straight horizontal lines. When I import the woofer’s frd file I get no change, still just straight horizontal lines in the top 2 graphs. What am I doing wrong?

My third question is about Paul’s Step #9 repeat for the tweeter. Do you have to complete the Impedance Model section with the tweeter’s Thiele/Small parameters to do the Minimum Phase Extractions?

[Wolf]

You can extract min phase from any file, .frd or .zma., without using the impedance modeler.

When you enter the driver parameters to simulate the woofer's impedance response curve, it's best if you import it as you measured it to see if there are any small peaks you should have present in the sim. This way you can transfer them to the RM via the EQ modules and keep them present.

When you add in the box parameters and vented or sealed, the overlaid imported zma should no longer be the same as the modeled zma. There are buttons below the plot that allow you to show in the pane what you want to see.

Use the modeled-box zma in your PCD simulation to utilize what your driver will actually have in your box.

If you are not seeing actual plots, then maybe your toolpak options have not been selected in the drop down menus.

Later,
Wolf

[Rand]

Wolf, Thank you so much for your help!

I don't know if you ever saw the Paul Carmody's instructions that I'm referring to, but he absolutely doesn't say to import your woofer's anochoic zma file to be modified. Maybe he figures it goes without saying or maybe he has something else in mind.

What parameters are needed to extract min phase?

When I have the time I'm going to give Jeff Bagby's Excel sheet another try. I have never designed a crossover before, but I've been using, programming and building computers since starting in the mid 80's and I know I have everything the Excel sheet needs and I get no errors, but it just doesn't seem to acknowledge an frd file. I built the computer I'm using in 09 and it was when Microsoft first released Vista in 64 bit and the Microsoft Office 2007 I'm using is also 64 bit. The reason I mention that is because I have heard people say they believe that Jeff's Excel sheet may have problems on 64 bit systems.

Thanks again,
Rand

[Wolf]

You don't have to import it if you don't want to. If the impedance has issues that make it spike in places, I'd want to know that they are accounted for.

You don't need parameters to extract phase. You click the 'extract phase from .zma file' button to the right of the box impedance emulator (or .frd if you want to extract from an .frd file), and save it back to the same file when completed, or save it to a new file- your choice. Done.

If you want another writeup to read, mine are linked in the Bible over at that other place. Paul's isn't the only one out there.

Have fun!
Wolf

[philpope]

I've been using Bagby's Response Modeler sheets and getting some interesting results. However, there is one big issue I don't understand. You can load in the measured resonse of a driver and then add in the effect of an enclosure and baffle. But the driver response will have been measured either mounted on an IEC standard baffle, or mounted in a standard enclosure (which will have its own baffle). Surely you have to subtract the effect of the baffle that the driver was measured on before adding the effect of the baffle you want to simulate.

Putting the dimensions of the IEC standard baffle into the sheet shows a 4dB boost at 200Hz and dips of -2dB at 500 and 1000Hz - so the effect of the measurement baffle can't just be ignored. most manufactureres don't clearly state the measurement method on their datasheets so you have to ask them to be sure how they have done it.

Can anyone clarify how to do the baffle modelling properly?

cheers
Phil

[Wolf]

Most measurements of drivers are gated and only good to about 500 Hz, and then the nearfield response is spliced in below there. This makes the normal spec graphs you see in most cases. This also negates the effects of the IEC baffle where the extreme edges of the surface no longer matter.

When doing measurements of drivers, I recommend just measuring them in the baffle intended for use, and then the IEC and Response Modeler can just be avoided. If you are using manufacturer specs and not real measurements, it is fine to use the IEC measurement with spliced nearfield into RM to adapt for the baffle you intend to use.

Later,
Wolf